1. Field of the Invention
This invention relates to an edge of dock leveler which acts as a bridge between a loading dock platform and the bed of a carrier and, more particularly, to an apparatus for operating an edge of dock leveler for positioning the dock leveler at selected positions relative to an adjacent loading dock platform. Additionally, this invention relates to a method of operating the apparatus.
2. Description of Related Art
Dock levelers for bridging a gap between a loading dock platform and a carrier bed are in widespread use for facilitating the loading and unloading of various types of carriers. Forklift trucks are often required to move from a loading dock directly into and out of the storage compartment of a carrier. In order to facilitate such an operation, dock levelers are used to compensate for any height variation which exists between a loading dock platform and the bed of a carrier.
Typically, an edge of dock leveler will have a center plate which pivots relative to an adjacent loading dock platform and a lip plate which pivots relative to the center plate. The lip plate will rest directly on the bed of a carrier when the dock leveler is positioned as a bridge. The manual effort required to pivot the center plate and lip plate is often reduced due to the use of counterbalance spring mechanisms which are employed to assist in positioning the plates. For example, U.S. Pat. No. 4,665,579 discloses a counterbalancing mechanism for an edge of dock leveler.
These counterbalancing mechanisms often do not provide sufficient force to assist an operator attempting to manually position the center and lip plates of a dock leveler. Accordingly, a large amount of strain is placed on an operator attempting to manually position the center and lip plates. This strain can result in back injuries to operators.
To prevent an operator from injuring his back and to eliminate the lifting effort required to position the dock leveler, a prior art system has been developed that does not require an operator to actually lift the center or lip plates. Instead, an apparatus is utilized so that an operator can position a dock leveler with a push/pull motion. Such an apparatus is disclosed in U.S. Pat. No. 4,689,846.
Several problems are created by the use of a push/pull apparatus to position the dock leveler because a dock leveler is designed to accommodate carrier beds of different heights. Typically, a dock leveler will have a service range from 5 inches above dock height to 5 inches below dock height. The currently available push/pull apparatus used on a dock leveler does not allow a dock leveler to be extended into a carrier which has a bed height in the top of the leveler service range, i.e., 5 inches above dock height, without giving up the industry standard of having 12 inches of the lip plate engaged on the carrier bed when the leveler is in the bridging position.
A second problem associated with currently available push/pull apparatuses is the inability to place and end load on a carrier bed without having to move the carrier to permit the leveler to move from its bridging position to its stored position. When a dock leveler is in its bridging position, approximately 12 inches of the lip plate are engaged on the carrier bed. An end load cannot be placed on the carrier while the lip plate is in this position. To fill the carrier to 100% capacity, the dock leveler is moved from its bridging position to its stored position where its lip plate will not be engaged on the carrier bed, but rather will hang in a pendant position relative to the center plate. A forklift can then move over the center plate and place an end load into the carrier.
The ability to place an end load into all loaded carriers is essential for trucking companies to operate profitably. Typically, truck lines operate on a low margin and the inability to efficiently place an end load in all trucks can make the difference between making a profit or a loss. For example, if an end load cannot be placed in a 40 foot truck and there are 4 feet at the end of the truck bed which are not utilized for carrying cargo, 10% of the truck's capacity is wasted.
The problem with currently available push/pull apparatuses such as that disclosed in U.S. Pat. No. 4,689,846 is that the apparatus is operative for extending the lip any time the center plate is pivoted to its rearward position. When an operator desires to recycle the dock leveler, i.e., move the leveler from its bridging to its stored position, to enable an end load to be placed in the truck, the center plate is pulled back to its rearward position and then pushed forward in an attempt to place the leveler in its stored position. When the truck is in the high end of the leveler's service range, the apparatus will continually extend the lip into the truck while the operator is attempting to recycle the leveler to its stored position. This prevents the leveler from moving to its stored position until the truck is moved away from the loading dock. Once the leveler reaches its stored position, the truck can be moved back to its initial position so that an end load can be placed on its bed. In a busy environment such as a loading dock, this procedure results in a time delay reducing the volume of material which can be loaded in a day and has a direct negative impact on profitability of the shipping operation.